Photonic microrings have been used to create waveguide switches. An example of such a waveguide switch 10 is depicted in FIGS. 1A and 1B. In FIG. 1A, an optical signal 12 is shown traveling via a first waveguide 14 (e.g., a silicon waveguide) from a point A to a point B. A second waveguide 16 crosses over the first waveguide 14. A photonic microring 18 is positioned adjacent the intersection of the first and second waveguides 14, 16. In FIG. 1A, the optical signal 12 is off-resonance with the photonic microring 18. In FIG. 1B, however, the optical signal 12 is on-resonance with the photonic microring 18, such that the optical signal 12 is coupled through the photonic microring 18 into the second waveguide 16, traveling from point A to point C. A bias may be applied to the photonic microring 18 to shift the frequency of the photonic microring 18 (e.g., toward and/or away from a resonance frequency).
One type of photonic microring 18A is depicted in FIG. 2. The photonic microring 18A includes a layered structure of n-type/p-type silicon. The frequency of the photonic microring 18A may be tuned by applying a voltage bias across the pn junction formed by the layered structure of n-type/p-type silicon. As shown in FIG. 3, the frequency shift is proportional to the applied bias.
Another type of photonic microring 18B is depicted in FIG. 4. The frequency of the photonic microring 18B may be tuned by changing the temperature of the photonic microring 18B. This may be accomplished, for example, by placing one or more resistors 20 in close proximity of the photonic microring 18B and applying a voltage bias across the resistors 20. As shown in FIG. 5, the frequency shift is proportional to the applied temperature.
It is difficult to manufacture photonic microrings with exact resonance frequencies.